Why a door closer slows down in cold weather

This is the oil, not a fault

Closing speed is set by how freely oil passes small valves. Cold oil is thicker and passes more slowly, so a door adjusted on a warm afternoon closes more slowly on a January morning. An external door sees the biggest swing because it sees the biggest temperature range.

Adjust for the season, not against it

Re-check the setting when the weather turns, and make small changes: half a turn is one increment. What to avoid is opening a valve a long way in winter to force the speed back. The door will then be too fast all summer, and backing a valve out far is how a hydraulic unit starts to leak.

When it is not the weather

• The door stayed slow when the weather warmed up again.
• There is oil on the body, the leaf or the floor.
• It got slower over weeks rather than with the first cold snap.
• It is slow and newly noisy at the same time.

Two different figures get confused here. EN 1154 sets a tested range: a closer conforming to it is assessed for temperature dependence from −15°C to +40°C, so cold performance within that band is part of what the standard covers rather than something each factory decides. Separately, our model pages state the lowest operating temperature the factory advertises for that model, which is their own figure and not a test result. Either way the number describes where the unit is meant to work; it is not a line below which a slower door becomes a defect.